Good to see this thread again. Reading it through, there's one (non-music) comment that shouldn't be allowed to become folklore. In Oct 2004, Reiver2 posted:

Mufflers and especially flat or "Dai" caps were and still are the most common dress for working men in S Wales, but yes it is cold!" (I'd asked if it was so cold in the mines that miners typically wore mufflers and caps while working.)

Scarves (usually white!) and flat caps were worn for walking to the pit, and may have been worn working on the surface, but you couldn't possibly wear them below.

I took a group of (mostly English) engineers down North Celynen pit after the 1974 strike. It wasn't a warm day, but I stripped to my underpants before I put on a light boiler suit. After 2 hours below, touring not working, I was a little warm (and very dirty). Those who had left shirts and trousers on were sweating hard. Most pits are pretty warm at the coalface.

Phil